The present invention relates generally to radiation therapy planning for the treatment of tumors, and in particular, radiation treatment planning for radiation therapy machines that provide independent intensity modulation of many narrow beams of radiation.
External beam radiation therapy involves the treatment of tumorous tissue with high-energy radiation according to a treatment plan. The treatment plan controls the radiation's placement and intensity, and thus the dose level to volume elements of tissue within a treatment volume so that the tumorous tissue within the treatment volume receives a sufficient dose of radiation while radiation to the surrounding and adjacent non-tumorous tissue is minimized.
Intensity modulated radiation therapy (IMRT) treats a patient with multiple smaller rays of radiation, each substantially smaller than the treatment volume and independently controllable in intensity and/or energy. The rays are directed at different angles at the patient and combined to produce the desired dose pattern. Typically, the radiation source consists of either high energy x-rays, electrons from certain linear accelerators, or gamma rays from highly focused radioisotopes such as Co60.
Radiation plays a central role in the treatment of head and neck (H&N) cancer patients. Conventional H&N radiation treatment is associated with substantial toxicity to normal tissue, and IMRT provides the opportunity to deliver radiation in H&N with enhanced conformance to tumor targets while diminishing the radiation dose to the surrounding normal tissue structures. Unfortunately, tumor target definition in H&N cancer is complex and the delivery of IMRT requires accurate and thorough target definition. Experienced H&N cancer specialists commonly consume several hours to fully contour and refine desired targets for a single H&N IMRT case. A substantial part of the complexity arises from the need to define not only the gross tumor volume (GTV) containing the tumor, but also to describe a contour containing surrounding lymph nodes. The lymph nodes can be very difficult to image and thus to distinguish from other tissue.
The complexity of the planning process associated with IMRT, a particularly in H&N IMRT may discourage the use of highly effect IMRT techniques.